I file several plan mod’s a year to keep tax refunds, and have yet to have a major issue. In each case I have clear expenses in mind (tires, home repair, dental/medical bills, etc.) and point out that the amount budgeted in the plan is not large enough to cover the unexpected expense. Keep in mind the definition of disposable income, “the amount not necessary for the health welfare or support of the debtor and dependents”. I make clear that it is impossible to account for a $1,500 repair bill in a $300 transportation line item etc…